Take our Classic Shortbread to the next level by covering it in melted chocolate-toffee bars and sprinkling shards of candy on top.
Preheat oven to 300 degrees, with rack in upper third. Sift flour and salt into a bowl; set aside. Put butter into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed until fluffy, 3 to 5 minutes, scraping down sides of bowl. Gradually add sugar; beat until pale and fluffy, about 2 minutes.
Reduce speed to low. Add flour mixture all at once; mix until just combined.
Using plastic wrap, press dough into a buttered 8-inch square pan. With plastic on dough, refrigerate 45 minutes.
Prick all over with a wooden skewer. Bake until golden brown and center is firm, 70 to 75 minutes. Transfer to a wire rack; let cool 10 minutes.
Put finely chopped chocolate-covered toffee bars and heavy cream into a saucepan. Cook, stirring constantly, over medium-low heat until smooth. Pour over shortbread in pan; sprinkle with about coarsely crushed chocolate-covered toffee bar. Let cool completely. Cut into 2-inch squares.
Store airtight up to 1 week.